Optical recording elements in which information is recorded by thermally deforming an optical recording layer are known. Such elements are useful in rapidly recording large amounts of digital information in a small area. These elements are also useful in recording video information.
Recording on an optical recording element is accomplished by an information modulated beam of high energy density radiation such as a laser beam. The laser beam is focused on the surface of the optical recording layer of the element. The recording layer absorbs energy from the laser so that a small portion of the layer is deformed, thereby forming an information bearing record element. The deformations may be in the form of pits, holes or other changes in the material. For example, if "bubbles" are formed, the material is "deformed" but not "ablated".
Generally, there is continuous relative motion between the laser beam and the layer and the recording layer so that as the recording laser is pulse modulated, discrete deformations varied in sizes are created in the layer. The size and spaces of these deformations constitute the encoded information.
The recorded information is also read back by a laser beam. In the read back cycle, the optical contrast from a recorded and unrecorded region is read by a laser beam via transmission or reflection. Most practical systems are based on reflection. If the recording layer is itself partially reflecting, then the optical contrast is obtained from light reflecting from the recording layer of the recorded and unrecorded regions.
In optical recording elements which are not highly reflective such as some heat-deformable recording layers, a metal reflective layer is used under the recording layer.
Pin holes tend to form in the metal reflective layer. This is particularly true in situations in which the metal film is in contact with organic layers such as organic supports, organic smoothing layers on the support or an organic recording layer. Pin holes in the metal reflective layer cause problems in the laser recording because light is not reflected in the area of the pin holes. This causes localized changes in recording sensitivity. The pin holes also give rise to higher noise and produces defects in recorded pictures. They also give rise to an increase in bit error rate during digital recording and read back.
Metal reflective layers having transparent ceramic overcoats are known, for example, from U.S. Pat. No. 4,195,312. The optical recording element disclosed therein comprises a substrate bearing a light reflective material such as aluminum and a layer of a transparent ceramic material such as silicon dioxide and an organic dye recording layer. The problem is that significant pin holes still form in the metal reflective layer resulting in the problems of low signal-to-noise ratio, high bit error rates and picture defects.